This invention relates to a protective relaying system for an electric power system, and more particularly to a system of the kind above described which is provided with means suitable for application to various types of relays which detect faults by digital means and deliver circuit breaking instruction signals so that these relays can be controlled by a common technique of arithmetic operation of system variables.
Electric power systems are very huge in scale and include various voltage levels ranging from a relatively high voltage to an ultra superhigh voltage. Various types of relays are used to protect various kinds of equipment in electric power systems, such as transmission lines, power station bus bars and transformers. Further, there are relays such as voltage relays, frequency relays and phase relays which are designed to operate by detecting various physical quantities. Thus, a great variety of protecting means are required for the electric power systems. The physical quantities such as the voltage and current in an electric power system are analog quantities. Therefore, most of the conventional relays employed hitherto have been of the hardware type provided with function of detecting faults on the basis of such analog quantities.
It is a recent tendency to attain digital control of relays in an electric power system by a computer for the purposes of achieving (1) the so-called simplification of hardware and (2) the possibility of changing the relay type by changing software which could not be achieved with the prior art method. However, various arithmetic operations must be carried out by the computer for the purpose of fault detection, and it is necessary to find a special arithmetic operation technique in order to control all the relays of various kinds as above described. A relaying system controlled by a computer and based on an arithmetic operation technique applicable in common to various relays has not been disclosed up to the present in anyone of the countries of the world.
A publication, for example, U.S. Pat. No. 3,569,785 entitled "POWER SYSTEM PROTECTIVE RELAYING BY TIME-COORDINATED SAMPLING AND CALCULATION" proposes that a protective relaying system having various relay characteristics can be realized by the technique of digital calculation. According to this U.S. Patent, however, physical quantities such as voltage and current of an electric power system to be protected are subjected to sampling in synchronism with a timing signal produced on the basis of one of these physical quantities, and the sampled physical quantities are converted into digital signals which are applied to a computer. While this patent provides a relatively common mode of calculation and is a useful invention, it is devoid of desired versatility in that a reference timing signal is required for the attainment of various calculations.